During the previous award period, transcellular biosynthesis was found to be a process which could occur in a tissue such as whole blood stimulated by a physiologically relevant process such as neutrophil phagocytosis. Transcellular biosynthesis of eicosanoids has been described as a process by which one cell produces a reactive intermediate such as LTA4 following cell activation and the reactive intermediate then is released from its site of synthesis to be taken up by an accessory cell and processed into a biologically active eicosanoid. For example, neutrophils can be stimulated to produce LTA4 which is transformed into LTC4 when platelets are co- incubated. The facile nature of transcellular biosynthesis is striking, considering the fact that if LTA4 is synthesized within the neutrophil, it must traverse two plasma membrane barriers before it can find the LTA4 synthase in the cytosol of the platelet. A seemingly unrelated observation made by several laboratories was that the critical enzyme in LTA4 biosynthesis, 5-lipoxygenase, appears to be translocated to phospholipid membranes during the process of activation of the cell. These observations and our interest in transcellular biosynthesis led to the development of a specific hypothesis that translocation of at least a portion of 5- lipoxygenase places this enzyme in a unique cellular position exposed to the extracellular milieu, so that metabolism of arachidonic acid can take place at the plasma membrane with release of LTA4 for transcellular biosynthesis by an accessory cell. this hypothesis does not require LTA4 to be made within the cytosol of the donor cell (such as the neutrophil), but in a position at the plasma membrane which facilitates uptake by an adhering platelet. Experiments to test this hypothesis are proposed including a study of the biochemical events of arachidonic acid metabolism during the translocation process and subcellular localization of 5- lipoxygenase using antibody and electron microscopic techniques. The process of translocation will be studied with reference to the recently described "priming" effect on the human neutrophil. Furthermore, the importance of cell-cell contact will be studied by modifying adhesion proteins on the neutrophil and platelet. The participation of other cell types and the potential synergistic effect of an immediately adjacent cell on the translocation process will be probed. Finally, the relevance of 5- lipoxygenase translocation in other lung cell types will be investigated. The main goal of these studies is to understand whether or not 5- lipoxygenase translocation and transcellular biosynthetic events serve as important route of communication between cells within the lung architecture.